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How long does it take on average for a control surface to deflect by one degree?
I know this should vary quite a bit (because of aircraft size / use / build / actuation / control surface weight), but I was wondering if anyone here could ball-park some numbers on how long it would take a control surface (aileron/flap/vertical stabiliser) to deflect by one degree on average.
I am writing a small aircraft simulator, and would like to try and use realistic numbers if possible.
If these figures are too variable, I would love to know some ball-park figures for some example aircraft if possible.

Is that a small simulator of aircraft, or a simulator of small aircraft? Or said differently, are you primarily interested in data for small aircraft? Certainly the Ikarus C42 will happily slam the flaps back to neutral if you aren't careful to hold the lever when releasing the lock. I wouldn't guess a duration, but it's a lot faster than you can react.

In a cable driven system, the only "delay" is the "slack" in the cables, which there should be none, so you can assume they react as quickly as the movement on the control column/yoke.

Yeah, what Ron said.  Make it equal to the rate of control movement and call it good.

...except that, if it's a PC simulator which uses a typical joystick, it will still be much faster than real: a full travel can be done in 0.1 s or so on a PC joystick. Still, this will likely cause much smaller error than many other unavoidable assumptions.

It depends how fast you move the controls.

With hydraulically actuated flight controls, the deflection speed is only limited by the maximum hydraulic fluid flow through the servo valve. I've taken some step responses of civil airliners in the past, and on-ground they can deflect full range in about 1-2 seconds.
For a mid-range passenger jet:

Elevator range = 42 deg, max no load deflection speed = 66 deg/sec
Aileron range = 40 deg, max no load deflection speed = 66 deg/sec
Rudder range = 48 deg, max no load deflection speed = 56 deg/sec

At higher airspeed the maximum deflection angle and speed become less due to aerodynamic blowback - by design, to limit the inertia forces on the airframe.

I once saw this when technics tested elevator after replacing one of the ELACs on A320. It was mesmerizing to witness elevators make full deflections several times at maximum rate. I’d say it was less than a second from neutral position from to full deflection but definitely it was lot faster than normal speed when using sidestick. I’d say normal full deflection on the ground takes some 2-3 seconds.

@busdriver Yes very powerful motion indeed. The data above is not from an A320, but from a comparable size jet with conventional mechanical cable type flying controls. The cited times are my projections, it takes some time for the control surface to be accelerated to maximum no-load deflection rate.

For a fighter jet, specifically the F-16 the max deflection speeds were:
Flaperons: 80 deg/sec
Rudder:   120 deg/sec
Horz.tail: 60 deg/sec
Note: The horz. tail value is from a Langley F16 simulator paper (TP-1538, you can find it on NASA technical document server), so might not reflect what it was on the physical plane, but it was 2 digits.
The source for the other 2 numbers is a flight control systems block diagram probably anno 1975. with a little googling you can probably find it on the Internet.


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Why is an ATC operational error called a "deal"?
Air Traffic Controllers who lose separation between aircraft call that event a "deal". Why?
When the Conflict Alert function was added to the computer system, it reported conflicts to the area supervisor.  Controllers came to know the feature as "Squeal-a-Deal", but no one could ever tell me why they're called deals.

They are called deals because they are situations which have to be dealt with. They aren't operational errors by ATC necessarily, they could be caused by an aircraft breaking a clearance.

It reminds me of the idiom, "What's the deal?"; which according to the free dictionary .com is a question asked of someone "to explain what they have been doing...." So as @GdD says, initially its investigational (could be serious or could be nothing), but "what's the deal" must be resolved one way or another.

For the same reason why further reduction of separation between said aircraft is a big deal? j/k.

I've never heard that term. It must be specific to whichever country you are talking about (the USA?) and the question should be tagged accordingly

As far as I know Deals are part of the US ATC system.

@J.Hougaard Yes, USA. The term was popularized by a comedian in the 80ies and 90ies named Jerry Seinfeld. His stand-up jokes often began with "Whats the deal with...(insert topic)." As in, "What's the deal with airline food", which he used as an intro to the subject then proceeded to discuss the topic and develop his joke for the audience.  Also, it can be used if someone is acting in a strange or rude manner, you can say "Whats your deal man?" Which is sometimes one step before a fist fight begins.

@Devil07 To clarify: I know the term "deal", I have just never heard it in this context before :) I added usa tag to the question

@J.Hougaard I totally see where you are coming from. If you know the meaning of "deal" it doesn't make sense in this context unless you're also familiar with the idiom "Whats your deal?"  Which, btw, is synonymous "Whats your problem?"

@Devil07 I once worked for a boss who declared "We don't have problems. We have opportunities to excel." The power of semantics.

The first time some of us heard this term was from a controller at a fly-in breakfast, perhaps in the early 80's.  One of the people in the group asked for clarification, and was essentially told that a "deal" was a "big deal" and that a report had to be written and reviewed, and it had the potential of being a factor in a performance rating.
The "deal" in this case was a maintenance truck which was still on a runway, after a 727 was cleared for takeoff.  The 72 driver saw the issue and delayed takeoff, but it was on the tapes, and there were people in the cab who saw it. So paperwork was filed.
Rumor had it that the processes for deviations were relaxed for the new controllers after the strike/firing of controllers under the Regan administration.

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How can I find out how much a passenger window of a Boeing 737 costs?
Where do I have to look to find out how much a passenger window of a Boeing 737 costs?

Sorry that I did not specify the aircraft model. I want to know for the Boeing 737 model. I need it in 90 ea. but want to know in the unit price.

Yes, it is. Actually I may need more but at the very early state it will be 90 ea. (and will increased).

I'm voting to close this question as off-topic, quotations cannot be provided.

Agree, I have already got the right response from "fooot". This question should be closed.

"I have already got the right response from "fooot". This question should be closed." That's not what closure is for. See What does it mean if a question is "closed" or "on hold"? and cast close and reopen votes privilege in the [help].

Just out of curiousity, did you accidentally break one and are feeling guilty about it, or what?

This page has declared values for part shipments, including one with the 140N2139-4, which is the assembly containing the seal, mid pane, and outer pane for the 737 NG. The declared value is 24,562 INR which is currently about 375 USD. A shipment of 20 also listed has a lower unit price.
For searching purposes GKN has part numbers in their catalog. You typically have to ask for a quote from suppliers.

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How much fuel did this Boeing 787-9 have on board for this flying display?
Once I saw how an Airbus A350 did a validation flight prior to an airshow and flew back to Toulouse from London Farnborough without landing/refuelling (distance: 550.57 mi (886.06 km)).
I thought that these aircraft must be very light to perform at airshows.
I then saw a video of the All Nippon Airways B787 at the Farnborough Air show 2016.
How much fuel did it carry to perform such a steep climb?

Even with full fuel, if they don't have passengers/baggage/extra crew on board they are still very light.

Looks like he is zooming after taking off: gain as much horizontal speed as he can, then pull up very steeply to convert some of the kinetic energy into potential energy. He only spends about 4-5 seconds at the crazy steep angle.
For zooming at these speeds, the mass is not very relevant: it appears in both kinetic and potential energy terms and cancels out.
$$\frac{1}{2}\cdot m \cdot \Delta V^2 = m \cdot g \cdot \Delta h \Rightarrow \Delta h = \frac{\Delta V^2}{2 \cdot g} $$
He just needs to take a longer take-off run at higher take-off weight to reach the same speed.

agree with 1/2mV2  =mAxdistance!   It is now in my toolbox as V2 = Ax2d, a useful conversion of kinetic and potential energy.  m does cancel out. Thanks!

The Airbus A350 and Boeing 787 are ultra-long haul aircraft with ranges in the order of $11\,000$ to $15\,000 \, \mathrm{km}$ (depending on variant). The flight from Farnborough to Toulouse is much, much shorter than that. Hence, the fuel on board was not even close to maximum.
Without any passengers and cargo, this would make the plane very light compared to MTOW (Maximum TakeOff Weight).

For two aircraft identical except for take off weight rotating at the same speed, the heavier one cannot maintain the same climb angle as the lighter one for a given amount of thrust.  There for, it is safer to perform a high angle takeoff with as low a weight as possible.
This concept is explained by comparing gravitational force mass x gravity in pounds to thrust force, also in pounds.  At any angle the lighter aircraft has the advantage.  Simplest case is straight up where net acceleration = ma - mg.  At lower angles where the vertical lift component of the wing is involved, total net lift requirement is still greater for the heavier plane.  Even if the heavier plane rotates at a higher speed, it's rate of speed loss will be greater once it starts to climb.

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How can an Airbus Beluga fly only with two engines and use short runways?
She could land and take off fully loaded on 2000 meters of runway at Hawarden Airport as seen here in this video. At my local airport the runway is 2500 meters long and an Airbus A300 is not allowed to land there. Maximum Airbus A321.

Despite its large and odd size, this plane (and similar variants like the DreamLifter), are usually very lightly loaded.  Their cargo is not terribly heavy, just very large and awkward (like airplane wings, or parts of aircraft bodies).

The large fuselage probably produces a great amount of lift. Airships derived part of their lift  with their body...

Why wound't it?

I asked a similar question here: https://aviation.stackexchange.com/questions/49018/is-the-airbus-belugas-safety-record-comparable-with-the-record-of-other-airbuse

This airplane is based on the Airbus A300-600. The maximum take-off weight of the aircraft is 155 tonne as published in the wikipedia. In addition, the the manufacturer has published the Aircraft Characteristics for the base aircraft.
If we assume that the aircraft low-aerodynamic aerodynamic characteristics has not been changed for the take-off phase (which the runway length depends highly on the aircraft lift and the engine power, and considering that the wing which contributes to the lift has not been changed and engines remained the same), then we can estimate the runway length for take-off and landing from that "Aircraft Characteristics" documents.
For the aicraft at its max take-off weight, in Sea/level, the required take-off runway length is predicted as 1800 m:

For the landing, the maximum landing weight is 140 tonne. Based on the document, the landing field length is 1554 m.

It should be mentioned that these aircraft are used for transportation of another aircraft sub-assemglies, which are large and light structures, such as wing, fuselage plugs, and tails. For this reason, the take-off and landing weight will be far lower from the above mentioned values, which permits them to operate on shorter runways.


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How was this flight authorized?
In this clip, we see a fighter performing risky manoeuvres at very low altitude around a densely populated civilian area.
What authorization would have been required for this and why would it be granted?

The portion of the video you linked to indicates that it takes place in Australia and the scenery seems to match. This means that the Australian Civil Aviation Safety Authority would be in charge of approving such flights. They provide a manual that describes air display administration and procedures. Other countries likely have similar procedures for authorizing such flights.
To summarize, the organizers of the event must identify individuals responsible for the safe execution of the event. They must complete a detailed risk assessment for the air displays along with plans for dealing with these risks and responding to emergencies.
These events are certainly more dangerous than typical flying, and accidents happen, but many people enjoy watching them without having to travel to the middle of nowhere.
For actual practice, which can be seen at points later in the video, they absolutely do use much more remote areas where the risk to the public is much lower. There are general rules for maintaining distance from people and structures, and pilots can and do face revoked licenses and jail time for blatant violations.
To your point about "almost stalling," it looks like the pilot is intentionally unloading the wings from the tight turn before rolling to pitch up, which actually helps to avoid a stall.

Per the manual, someone must be designated as the Display Organiser, with responsibility including event site and display management:

conduct and compile risk assessment
where designated airspace is identified as a risk treatment, compile and submit Form 1284 to CASA
site suitability
spectator safety
extended third party safety
documentation checks and display insurance confirmation
pilots' display programs (both normal and weather-restricted programs)
in consultation with the Display Coordinator and Ground Coordinator the development and implementation process of the Emergency Response Plan (ERP)
responsibility for the safety of spectators and third parties not associated with the event. This is one of the most important responsibilities placed on the Display Organiser for which personal liability may well be a significant factor.

In addition, "reasonable steps must be taken in the planning and execution of the event to provide safe outcomes."
There must also be a Display Coordinator that specifically takes responsibilty for the airborne displays:
The Display Coordinator is responsible for:

flying discipline and coordination of acts within the display for the safe and effective execution of the event
the compiling, approval and modification of individual flying routines in the interests of safety commensurate with pilot experience and qualifications
the cancellation or modification of the flying program in the event of unsuitable weather or other such conditions, such as aircraft unserviceability, accident / incident and Knock it off procedures
confirming minimum heights, maximum speeds during display
stipulating weather minima criteria
conducting pre-display briefing.


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Why do aircraft have an unusable amount of fuel?
I learned from this question that a Cessna 152 holds 5.6 litres of fuel that it can't use.
Why would it be designed to hold fuel that it cannot burn, especially since water contamination of fuel is a concern?

5.6 liters doesn't seem like a lot of fuel to be worried about...

It's not that I was worried about it, I was confused by it until I read the explanations below. Now it makes sense.

unusable fuel is just like unusable toothpaste.

@kevin: So it gets dumped along with the rest of the engine whenever the trip is over?

@Mehrdad: After a flight the tanks can simply refueled. If the wings / tanks have to undergo maintenance, then it may be necessary to drain out the unusable fuel.

@kevin: I know, I was joking. I was trying to point out that it's not very similar to the toothpaste scenario.

@Mehdrad: You can refill toothpaste (-:

It's similar in the fact that both are equally useless - you can work to get at some of it. But only if you really need to. :-)

It's not a characteristic unique to airplanes. Any fuel tank that doesn't drain from the absolute lowest point is going to contain unusable fuel.

Pilot here (with Cessna 152 hours) as well as an engineer who made it most of the way to an Airframe and Powerplant technician license at one point in life.
There are several reasons that conspire to produce 'unusable fuel':

Fuel tanks on airplanes have complex shapes - they include baffles and other walls (with holes in them) to prevent oscillations from building up during in-flight movement. Sometimes these baffles are even engineered into the tanks late in the design cycle as testing finds oscillation issues. These baffles result in 'geometric trapping' of fuel in nooks and crannies.
Drawing fuel from a fuel tank is more complicated in a plane - cars are pretty much flat with minor tilts while airframes can have all sorts of odd and sustained directions that the fuel wants to go due to acceleration. Imagine an extended tilted spiral while descending - that fuel experiences far more lateral acceleration over a longer time period that a car would have. Getting the fuel system to pull fuel out from these different angles is challenging (note that I've picked a non-aerobatic maneuver for which the Cessna 152 of your question is qualified here).
All of this is a cost/complexity tradeoff - solutions exist for 1 and 2 above - fighter jets use fuel bladders that have pressure bladders arranged to squeeze the fuel out so that they can get almost all the fuel even at high G-forces and unusual angles. Aerobatic planes have similarly more expensive and complicated systems than the old and cheap Cessna 152.

There are other considerations as well, but mostly it comes down to whether the plane in question can justify the cost and effort to get every last drop of fuel.
Things get even more complicated in rockets - the moon rockets (properly the Saturn 5 although it was an upper stage specifically) had special extra engines called ullage motors whose only job was to give the stage a little boost in space to push the fuel towards the rear of the rocket so that the main motors could draw fuel and start.
Addendum edit: @supercat below - the definition of unusable fuel is set by federal aviation regulation part 23, section 959 (FAR 23.959) and basically is the worst case under "intended operation" for the particular plane. Since the Cessna 152 is not aerobatically rated, for example, the unused fuel is defined as the fuel level where SOME intended maneuver would be capable of causing a fuel system error. In practice, especially in flat level flight, some of that unusable fuel would be available for use although you are not supposed to plan to use it in your flight planning.

Ad 2). Actually car may have pretty serious tilt when cutting corners or braking abruptly. Tires have coefficient of friction 0.8-1.0 on dry road, so the effective gravity vector can tilt to some 40-45°. On the other hand airplanes don't have anything capable of producing lateral force comparable to lift, so their effective gravity vector can't till nearly as much and any such forces are avoided by pilots as they cause lot of drag too. In coordinated flight the slip-skid ball is centered and slip-skid ball is just a ball level!

On the other hand of course the fuel tanks on aircraft are much wider, so any lateral acceleration has bigger effect in them.

What about any dirt or water that sinks below the fuel output valve and therefore doesn't get into the engine? Isn't that a reason as well?

RE #2: "Aerobatically", a spin is an excellent way to move fuel around in the tanks. In fact, a good spin around the CG will move the fuel to the outside of the wing tanks; it'll move anything to the left or right of the CG further to the left or right. A Cessna 152, having gravity feed fuel lines at the wing root, I believe will actually stop running after about 6-8 or so turns, since you've essentially stopped feeding fuel to the engine. It's been a while since I've conducted spin training in that aircraft. And never to the degree of moving unusable fuel around like that. :-)

@Jan Hudec - good points, I actually had an answer about 3x as long originally and tried to keep it simple. In coordinated flight the acceleration pull will indeed be oriented 'down' to the plane's frame of reference. However, the airframe engineers cannot rely on this for fuel availability calculations because valid maneuvers like side-slips (approved for losing altitude) do not require this coordinated condition. If you always 'step on the ball' and stay coordinated you may have access to some of that fuel which is rated unusable - though I wouldn't count on it for planning!

@Shawn - Yes! And some pilots are taught maneuvers that are specifically used to move fuel around the tanks. There is a good bit in 'Lost Moon' about how the astronauts used the maneuver rockets from the lander to perform an ullage burn for the command module (if I recall, I might have the particulars wrong). A friend who flew cargo jets for the military told me about a fancy tilt-tip they used to redistribute fuel, though I can't even recall what aircraft that was for.

Does the "unusable" fuel spec represent fuel that would never be usable, or instead represent a guarantee that at most 5.6 liters will be unavailable under conditions of roll, pitch, and acceleration that one might want to use to land the airplane?

I always thought that "unusable" fuel was the fuel that couldn't be accessed through normal operations and conditions. Though I will say that if you're ever trying to actually use the unusable fuel, you've probably got better things to be worrying about. :-)

See addendum above. unusable fuel is the worst case - so if you had that much fuel during the worst maneuver (approved for the aircraft) for the fuel system you need to have at least the rated unusable fuel to prevent a problem.

Would a funnel shaped fuel tank be feasible in airplanes to make all the fuel pass through the engine? (sounds ridiculous now that I think of it)

@shortstheory - Where would we put such a funnel shaped fuel tank? The fuel tank is normally the inside of the wings in order to have large storage volume without adding size as adding aircraft size = more drag. So there are strong aerodynamic reasons for the common tank shape. Extra fuel tanks, however, are often put in the passenger cabin, have different shapes, and often have lots less unusable fuel issues.

@EzekielKruglick thank you I forgot about the tanks being mostly in the wings!

especially since water contamination of fuel is a concern?

That's one of the reasons. Fuel floats on water, so water collects in the bottom of the tank, along with other gunk. By not taking the last dregs of fuel from the bottom of the tank you avoid putting this stuff into the engine

This may be true in some systems but others do try to take the last dregs of fuel from the tank. The fuel pick-up ports in many Cherokees are right by the sump drains (near the lowest inboard point in the fuel tank) so you'll probably wind up getting water before you get avgas. In that system it's the gascolator's job to get rid of (or more accurately, hold on to) water and "gunk" - in fact the gascolator bowl is about half of the unusable fuel capacity in some models.

@voretaq7 I imagine that's why you drain a bit off each tank in a Cherokee during the flight prep.

@slicedtoad Partly, but you check your fuel for water even in tanks that tend to hold more "unusable fuel" because of their design, and those tend to have more sump points right where the unusable fuel collects (e.g. the 800 sump points on some Cessnas with fuel bladders). The fuel pickups are still usually pretty low in the tank, which just means water that moves around while you're maneuvering might slosh out of one spot where it's harmless and get close enough to the pickup to be drawn into the engine.

I would guess that any aircraft that doesn't use a fuel pump (and lots that do) would keep the fuel inputs at the lowest point of the tank so that gravity can reduce the work of the pumps. @voretaq7 has it right.

Almost any system that moves liquid around will retain a certain volume. In your case, there are various bends in the pipes and some of those bends go up. Yes, it's gravity-fed but notice the shutoff valve on the floor. Now notice the level of the carburetor. Any fuel below the level of the carb bowl is unusable, as we have no way to push it through the rest of the plumbing without more liquid behind it.
If we turn to things with a pump the unusable quantity can go up, a lot. The volume of liquid between the pump and the final destination would be considered unusable for the same reason - once the pump is dry we can't move it along anymore.
One restaurant manager I used to know installed a metered drink dispensing system. All the booze is in the (locked) storage room, the bartenders push a button and exactly one ounce comes out of the tap. The only complaint he had was that the system cost $500 to prime, per item, and he had to keep thousands of dollars of "unusable" alcohol on the books.

This is the best answer to the question as asked.  If nothing else, the fuel that clings to the walls by surface tension is not usable, so there will always be some.  Even if the designers work hard to minimize it, it will not be zero.

The term "unusable" is a very special definition. It comes from a specific test described in FAA FAR Part 23. It is not the same as the common sense meaning of the word "unusable".
For single engine light planes like Cessna 152, FAA FAR Part 23 requires the available  fuel flow to be 125% of max engine consumption. 150% for pure gravity feed systems.
 At certification test the fuel flow is measured while the level is dropping in the tanks. As soon as the flow rate goes below 125 or 150 % all remaining fuel is declared unusable. This shall be done with the plane supported in  climb nose up atitude.
So, the formal term "unusable" means this last amount of fuel might be unavailble in a nose up attitude at full engine power.
In level cruise you can normally empty the fuel tanks to the last drop.

I pitch in blind here, but I believe in some instances fuel is circulated for heat exchange.

Something like the SR-71?

Not in any GA aircraft I know of.  Possible in airliners and military aircraft.

Common enough in larger aircraft to have a fuel/oil heat exchanger, cooling the oil & warming the fuel enough to melt any ice crystals that formed in the fuel as it cooled to something close to OAT up at high altitude.  The problem being averted isn't water in the fuel per-se, but clogging a fuel filter with the crystals.  All that said, this is simply more plumbing in the fuel line, and the dynamics mentioned in other posts wouldn't change all that much with or without the heat exchanger.


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How frequently do aircraft get struck by lightning?
We have several questions here about what happens to an aircraft when it gets struck by lightning (e.g. this question), and at least one answer from a former pilot who knows he was struck once and thinks he was struck other times. How frequently do aircraft get struck by lightning?
Additional commentary on how do you know you've been struck would be appreciated, but I'll make that a separate question if it's more appropriate.

Lightning strikes airplanes commonly, and for modern airplanes, it is not a big deal. Although, to put a definite number is not realistic, as it is not analogues to how many miles a car runs with a full tank.
On average, it is estimated that lightning strikes an airplane once every 1000 hours of flight time.
Although, as mentioned:

The frequency of lightning strikes that an airplane experiences is
  affected by several factors, including the geographic area where the
  airplane operates and how often the airplane passes through takeoff
  and landing altitudes, which is where lightning activity is most
  prevalent.

Every 1000 hours of what? Somewhere in the world, a plane is struck every 1000 hours? Each plane is struck every 1000 hours? Each plane is struck every 1000 hours of flight time?

It is estimated that on average, each airplane in the U.S. commercial fleet is struck lightly by lightning more than once each year.

Edward J. Rupke, via Scientific American.

The Federal Aviation Administration estimates that on average, lightning hits each airliner in U.S. service once a year.

Washington Post
It looks like commercial airliners get struck about once a year. I was also able to find an FAA source, but it doesn't look like it's the original source.


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What is the difference between "sensitive" and "non-sensitive" altimeters?
In this answer reference was made to "sensitive" and "non-sensitive" altimeters.
What is the definition of each, what are the differences, and why would one be used in preference to the other?
And why isn't it called an "insensitive" altimeter?

In response to your last question, all altimeters are insensitive, they have no regard for your feelings.

All altimeters are "sensitive" to some extent (an "insensitive" altimeter would be one where the internal pressure-sensing mechanism has failed: the pointer wouldn't ever move).
What the FAA calls a "sensitive altimeter" is simply more sensitive than a regular (now often called non-sensitive) one:

Non-Sensitive altimeters have a 1000-foot scale (200-foot tick marks) as their most precise display.
Sensitive altimeters have a 100-foot scale (20-foot tick marks) as their most precise display.

The sensitive altimeter in "glass cockpit" displays go even further, often having 1-foot resolution on a digital read-out.

Let's look at some (analog) examples:

Non-Sensitive Altimeter, not adjustable for barometric pressure

This altimeter is similar to what you'd find on an old Piper Cub: The scale is marked in thousands of feet, with ticks every 200 feet.
This altimeter is not adjustable for "barometric pressure", but it is adjustable: The little knob on the bottom rotates the face of the altimeter. Put field elevation under the needle before you take off and it should be a reasonable approximation of your current altitude for the duration & distance of a typical Piper Cub flight.
These altimeters can only be "set" on the ground, because you need to know your elevation to set the position of the face or needle.

Non-Sensitive Altimeter, adjustable for barometric pressure

These show up from time to time: It's a non-sensitive altimeter (same scale markings we saw above), but it's adjustable for barometric pressure. The Kollsman window on this one is marked in inches of mercury.
When you turn the knob on this altimeter the needle moves and the barometric pressure that corresponds to "zero feet" shows up in the Kollsman window. This makes it easier to read than the previous example, and easier to reset in flight based on radio information: You can set the local barometric pressure (QNH) in the Kollsman window and get your current altitude without having to be on the ground at a known elevation.

Sensitive altimeter, not adjustable for barometric pressure

In this sensitive altimeter you can see that there is a 100 foot scale (large pointer), and a 1000-foot scale (small pointer).
This is a bit of an unusual example: It's a sensitive altimeter that is NOT adjustable for barometric pressure (the knob simply adjusts the position of the pointers, and you set it to field elevation like you would with our first example. It can't be easily reset in flight as you need to know your current altitude to reset the altimeter correctly.

Sensitive Altimeter, adjustable for barometric pressure

This the altimeter most pilots are used to seeing in a "steam gauge" panel: It is a sensitive altimeter (note the 100-foot scale pointer), and it is adjustable for barometric pressure (note the Kollsman window, marked in millibars in this example). This is the type of altimeter required for IFR flight.
This one happens to include 3 pointers (100-foot, 1,000-foot, and 10,000 foot), because it's calibrated to 20,000 feet.

As with most aviation products there is a Technical Standard Order (TSO) behind altimeters which would get into all the specific details of the differences.
For sensitive altimeters it's TSO C10 (I believe C10b is current).
I'm not sure if there's one for a non-sensitive altimeter.

Re the non-Kollsman meters, presumably one could adjust them in flight by keeping track of the pressure changes and adjusting the meter by the matching number of feet?

@IanF1 Fixed (I thought I stole two altimeters marked in millibars, guess I didn't :-)

@IanF1 Re: adjusting altimeters in flight by adding/subtracting the number of feet corresponding to the pressure difference you could certainly do that: Write it down and do the math. We'd screw it up pretty universally though (most folks would know "0.1 inches of mercury is about 100 feet", but actually it's 87 feet and some change - that can be a noticeable difference over a medium-length flight).

P.S. the original TSO-C10 (and I presume C10b) does mandate that a TSO'ed sensitive altimeter have a Kollsman window for setting the barometric pressure (the TSO has always punted to a SAE standard, but the original actually includes a copy while the B revision just says "go see SAE standard bla".)


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Do jet engine exhausts usually glow orange?
In these two lovely images:
Source: Wikimedia Commons
Source: wvi.com
The exhaust end of the engines are glowing bright orange from being so hot. Do they get that hot during normal flight operations, or are they hot because the engines are statically mounted for testing and have (relatively) minimal air flow to cool it?
If it's normally this hot, what is the exhaust made of, and how is it insulated to keep it from melting the nacelle around it?

Those are afterburning engines that dump raw fuel into the exhaust stream to produce additional thrust. Specifically the engines you posted are ramjet engines used in the SR-71. The SR-71 engine was basically 2 engines in 1, one turbojet for lower speed and then at higher speeds a ramjet. What you have posted are images of the turbojet in afterburner, so yes it can get that hot. The SR-71 was made with titanium materials that have very high melting points.

Closely related: How are temperature differences handled in a jet engine?.

@RonBeyer - not disagreeing or arguing your points at all. My question of "is that normal for flight ops" still stands...

I think @RonBeyer is trying to say that you've picked two pictures of a very special engine for a very special aircraft. There is nothing "normal" about the SR-71. What is "normal" for the SR-71 is utterly absurd for any other aircraft... Take for example, the fact that it leaks fuel on the ground. If it didn't, when the material expanded due to the skin heat generated in flight, it'd pop like an overfilled balloon.

I have personal experience only with pulso jets on model aircraft. Yes, they, too, would glow orange in static operation, but when airborne the outer flow would cool them sufficiently to become "dark" again.

Here is an image of the F136 in a special test chamber that simulated flight conditions, including flight pressure and flow. As you can see the afterburner is not glowing orange. That being said, many engine internals, especially the combustor and HPT glow orange the entire time the engine is running.

Also engine cooling design as significantly improved in the decades since the J58 was developed and massive importance has been placed on reducing IR signature.

@PeterKämpf, I suppose that would be specific to model engines though since full-scale engines would be primarily cooled by the bypass air and that shouldn't differ significantly between static and flight run or even be a bit colder in static run.

@JanHudec See my second comment, cooling has improved a lot and IR signature reduction is much more important today than when the J58 was developed. But both pictures show the outer nozzle casing, not a combustor liner. Modern nozzles use bypass air to reduce IR signature and case temperatures, but the J58 used compressor bleed air that was already hot (especially in flight). Besides the temperature difference there is a lot more by-pass air the compressor bleed air.

I used to lie under the departures and watch aircraft take off.. on most airliners you wouldn't see anything but when a fully laden 747 took off you would see the inner part of the exhaust dimly glowing. One that sticks in my mind was the CI 747-200F..

Both images you posted are of Pratt&Whitney J58 afterburning turbojet that was used on the Lockheed A-12 and Lockheed SR-71 aircraft. That engine ran particularly hot.
The engine was designed for operation at Mach 3.2. The efficiency of turbojet increases with speed, but only to a certain point and somewhere above Mach 2 it starts to decline. However efficiency of afterburner continues to increase, so this engine was designed to operate continuously with afterburner and to generate higher fraction of power in the afterburner than other engines.
The afterburner combustor liner was able to withstand temperature up to 1,760°C (3,800°F). The core of the flame was much hotter still, but a colder air was fed along the walls, like in all turbine engines, as explained here. The engine was also cooled by incoming fuel similarly to how rocket engines are.
Additionally, at the top speed, the compression heating as the air was slowed to subsonic speed in the inlet heated it to over 400°C (800°F) at the compressor face already. Since in the static test the air was not that hot, the engine might have actually ran a bit colder in the test than in normal operation.
This was however specific to this one engine. The compression heating is negligible at subsonic speeds and grows faster at higher Mach numbers. Most supersonic aircraft fly around Mach 2, where the effect is already noticeable, but not nearly as pronounced. For most engines, they run at roughly the same temperature in test as they do in normal operation. It just isn't as high as in this special case.

Q1:  Yes the afterburner pipe and nozzle interiors can hit upwards of 1800-2000° F during full throttle operations.
Q2: Most engines have ceramic linings in the afterburner can and nozzle petals to protect the metallic parts from the high heat.  In his book Sled Driver, Maj Brian Shul remarks about witnessing J58 engine test runs post maintenance out at Beale AFB, where the engines were brought up the maximum power for several minutes and then shut down.  He stated the engine jet pipes would glow orange hot during operations (and took the photos to prove it!), yet within a minute or so of shutdown the ceramic linings were cool enough to touch!

To supplement Jan Hudec's answer, you are also looking at the engine casing itself.  When the engine is installed in the aircraft there is additional nacelle material surrounding it so that even at full power the metal glowing will not be seen looking at it from the side.  (although in afterburner you will see the flame)
But the answer is yes, a typical jet engine will heat up enough to glow during normal flight operations.  However, is it much much dimmer than your photos, really just a dull orange.  And you usually only notice it if you are looking almost directly up the tailpipe at the turbine section.


text:
What is an augmentor wing?
What is an augmentor wing in the context of STOL aircrafts? and is it still used today? This seems to be a term that I can only find in NASA aerodynamics (specifically powered-lift) research papers in the 70s and 80s. Example reference paper: https://apps.dtic.mil/dtic/tr/fulltext/u2/a177750.pdf

In a blown wing, such as blown flaps, air is driven by the engines through ducts in the wing and out through various orifices to boost the airflow over the wing. This helps increase lift, especially to give good STOL performance at low forward speeds.
The augmentor wing takes the sophistication a stage further by arranging the air outlets so that the flow draws in or entrains ambient air into the wing flow, further increasing or augmenting mass flow and the efficiency of the system.
A typical example was the DHC-5 modified with an augmentor wing; a little bit about it is given on Wikipedia. The Rockwell XFV-12 was a supersonic VTOL fighter prototype, which blew the air directly downwards through vertical slots in the wing, however it did not entrain as much additional air as expected and lift augmentation levels were disappointing.
The system has never reached operational use, mainly because the weight, complexity and cost have never been justified by the performance gains.


text:
Can I land a plane in a field in the UK and Republic of Ireland?
So I already saw this question here for the US, but I live in the UK and quite close to the border with the Republic of Ireland (ROI). We have property over the border in the ROI and I was wondering if I could fly back and forth by using the fields to take off and land in a small plane like the SD-1?

Welcome to aviation.SE! If you're new to the site you might find the [tour] is helpful. I reworded your question a little to hopefully make it a bit clearer; if I got it wrong then feel free to roll back my changes or edit further yourself.

Is the question about crossing borders (either generally or that specific one), landing off-airport on your own property, or the specific aircraft named (or experimental craft generally)? If more than one of those, it may be best to ask each piece as a separate question.

Well you'll need permission from the land owner to land and take off.  Also, there's a planning rule in the UK that says you can use land for only 28 days each year for flying if you don't have specific consent for an airfield

Well my family owns a some land in ROI so even if the plane was only flying around there for the summer?

Also @daveGremlin what do you mean “specific consent”?

@ddoherty958 - sorry, I meant specific planning consent from the local authority.  There's a recent discussion that touches on the subject here: https://forums.flyer.co.uk/viewtopic.php?f=1&t=107244

Ireland allows ECAC-registered experimental amateur-built aircraft to operate in its airspace for up to 28 days at a time, as explained here, as long as your aircraft is legal to fly in the country in which it is registered. This link also contains information on what to do if you plan to stay longer than that.

Thanks. I guess that answers it. Up to 28 days for a home built aircraft in the ROI. We are the landowners so no worries there. The summer looks eventful!

No, you can't shuttle back and forth over the border from one field to another between the UK and Republic of Ireland (RoI) because of regulations. The RoI requires you go through an airport of entry when entering and leaving the country, see the IAA AIP Gen 1.2-1:

Aircraft landing in the territory of Ireland must first land at an
  International aerodrome or at a licensed aerodrome where customs and
  immigration facilities are available. Aircraft departing must finally
  depart from an International Aerodrome or from an aerodrome where
  customs and immigration facilities are available.

The UK has no requirement to take off and land from a customs airfield, you can go and land from anywhere (from a customs perspective), which is handy. You do have to notify Special Branch at least 12 hours ahead of your flight if you are going to and from the RoI, channel islands or Isle of Man and give them details on who is going and where you are going from and to. You must do this even if you plan to go to and from a customs airport on the UK side.
In the UK you can use a field up to 28 days a year without getting planning permission from the council, provided you own the land (or have permission from the owner) and it is safe to do so. If you plan to do more than 28 days you'd need to talk to the local council and the CAA. I don't know about the RoI though.

Can you provide a link to the Irish customs regulations that you mentioned?

Sure @Pondlife, see my edit.


text:
How can I correct an expected climb rate for density altitude?
If a flight manual (for a naturally aspirated piston engine plane) gives a figure for a best climb rate at standard temperature and pressure, is there a way to adjust that figure for a different density altitude?
(I'm thinking there must be, but I can't find such a formula anywhere. Assume the same speed, weight, etc.)

There are several tools which can do what you want.  Some electronic flight computers will perform the calculation, and here is a mechanical one which will:  https://www.mountainflying.com/products/apr_304
Ed Williams has a graph, which is almost linear, showing the impact on BHP with differing DENALT.  See page 6, http://edwilliams.org/smxgigpdf/mfly2.pdf
Essentially ROC is a nearly linear function of excess HP, so you could use the slope of Ed's chart to predict your climb rate at varying DENALT.
Addendum 1: Approximate figures I use for NA aircraft are:
Time Fuel Distance +10% for each 10C
TO roll +10% for each 1000ft DENALT
ROC -10% for each 2000ft DENALT  (a conservative number, as 7% is probably more accurate)
ROC -10% for each 20C  (also conservative, as 7% is probably closer)
These are just generalized performance figures I use, and I do not supply their derivation, etc.  Check them against the POH / AFM or manufacturer test data for your aircraft.
Addendum: This article, while it disagrees with my generalized TO roll estimation, may provide some supplemental understanding:  https://www.flyingmag.com/technique/tip-week/calculating-density-altitude-pencil

Can you explain why the answer isn't to use the density altitude with the standard table? For instance, if my true altitude is 5kft but the density altitude is 10kft, doesn't that mean the 10kft (at STP) performance figures should be correct as-is? I thought that was the entire point of the calculation.

@StephenS perhaps the question has some ambiguity.  I interpreted that OP had data points for STP and wanted to adjust for different DENALT. While I didn't give an equation, I provided ways the data could be interpolated.  Perhaps the question could be clarified. I would be happy to correct or modify the answer accordingly. Not all POH / AFM include performance charts.

mongo thanks you interpreted my question correctly.
@StephenS indeed this POH doesn't have that performance table, just a single figure for STP at sea level :(

Does my answer adequately address your question?

That depends on what the POH for your specific aircraft includes. For example the POH for the PA-28 Warrior has a correction chart for calculating just that. In this case you need to use pressure altitude and local temperature (which combine to density altitude anyway).

Its important to use the POH for the specific aircraft as things like engine modifications, installed propellors and other changes to the airframe can greatly affect the numbers. These changes may only be reflected in the POH for the airframe its self and a copy found elsewhere may be inaccurate. Correction charts and your POH may also include pertinent information about operational limitations during a climb as well.


text:
Can I convert an FAA medical certificate to a Canadian one without visiting an AME?
I currently hold a first class FAA medical certificate. Can I transfer to a Canadian medical certificate without meeting with a Canadian AME?

(2) The applicant may obtain a TCCA Medical Certificate as follows:
(i) The applicant may submit either the original or certified copies
  of FAA medical examination reports directly to the Civil Aviation
  Medicine Branch of Transport Canada, Headquarters in Ottawa for
  processing and assessment;

or

(ii) Applicants may complete an aviation medical examination by a
  person who is considered to be a medical examiner with the authority
  to conduct aviation medical examinations pursuant to CAR 404.16

Welcome to aviation.SE! I edited your question a little and added quotes where I think you were quoting some document. If I got it wrong please edit again as needed!

You cannot convert an FAA medical certificate directly into a Transport Canada medical certificate. However, you can obtain the Transport Canada medical certificate on the basis of the original or certified copies of FAA medical examination reports by submitting them directly to the Civil Aviation Medicine Branch of Transport Canada, Headquarters in Ottawa for processing and assessment. If they are deemed acceptable, the certificate would be issued in Canada without having to start the process with a Canadian AME. For more information, see Transport Canada Advisory Circular (AC) No. 401-001, "Application Guidelines for Aeroplane FAA to TCCA Licence Conversion Agreement".

then just simply send FAA medical examination reports to Branch of Transport Canada? I've tried to contact them, it is really hard to contact them.

Follow the instructions of section 7 of the document for which I provided a link. Here is a direct link to section 7. And if this answer provides the info you needed, don't forget to accept the answer. :) http://www.tc.gc.ca/en/services/aviation/reference-centre/advisory-circulars/ac-401-001.html#toc70


text:
How do I renew my ability to fly after 40 years?
I am 83 years old and it has been over forty years since I piloted an aircraft and would like to go back to flying again. I hold a single engine rating and had flown several hundred hours, but my log book is long gone. Much of my time was ferrying new Cessnas from Kansas to Houston for a dealer. Other than a physical and a checkride what would I realistically need to resume flying again without endangering myself or others?

Hi J W Clampitte, welcome to the forum.  Just FYI, our group insurance is limited to pilots under 80 years of age.  I think the premiums go up steeply for older flyers, you might want to check that

Much has changed in 40 years, including airspace designations, ATC communications, and new regs.  If I were you I would take an online Private Pilot Ground School to learn about all the new changes.  These courses are not too expensive and it well worth the money.
The AOPA does have a Rusty Pilot Seminar as well (link).
Also it might be worthwhile just to sit in the passenger seat of a plane for a while to re-familiarize yourself with how it all works.

Thanks, I have ridden along a couple of times with a friend and that is what stirred up my curosity to fly again.  Health is good and I will take you advice.  My flying was mostly VFR with a little ADF thrown in.

ADF, those are disappearing fast. Moving map GPS is what most things are transitioning too. Get a nice iPAD with Foreflight software, GPS receiver, something new to play with.

Does Foreflight run on other tablets? https://www.foreflight.com/ I don't believe it does. IPad with cell-phone is suggested (don't need a phone account, just need the cell-phone for the GPS)  https://www.foreflight.com/support/buying-guide/

@CrossRoads: No, it doesn't, unfortunately.

Do you even need the cell-phone if you have an LTE-enabled iPad? They have GPS hardware.

@T.J.L:  If you have an IPad with a GPS then you don't need a cell-phone.  However, if you pair your foreflight with a Status is uses WAAS GPS and is more accurate.

Certificate, Medical and Flight Review
FAR Part 61 explains what is needed to exercise the privileges of your pilot certificate.  For this answer, I will assume that you are certificated as a private pilot.
Certificate:
Your certificate does not expire, so, presuming you are still in the FAA database, you should be able to pay a small fee to have a duplicate sent to you, if necessary.
Medical:
Here you have some options.  As a private pilot you may now operate under sport-pilot regulations (day-VFR, restrictions on aircraft seats, weight and stall speed).  The basic med rules are still less restrictive, and of course you may still obtain a third class medical for full privileges.  If you think you may have trouble with a third-class medical, it would be good to research your options before scheduling an examination.
Flight Review:
Finally, you must have a CFI endorse your competence with a flight review.  This is normally a two-hour affair, one in the air and one on the ground, but in your case, as others have said, you may want to study and perhaps take several refresher flight lessons.

If you're still in the system, you can request  a duplicate certificate here  https://www.faa.gov/licenses_certificates/airmen_certification/certificate_replacement/

You may be able to get a Basic Med certificate vs Class III medical. More info here  https://www.faa.gov/licenses_certificates/airmen_certification/basic_med/  and https://www.faa.gov/documentLibrary/media/Form/FAA_Form_8700-2.pdf

@CrossRoads Can't get BasicMed if you haven't had a 3rd class since before 7-14-2006. Have to get a 3rd class first

Thanks. I had taken ~12 years off, and then just a Class III without knowing the Basic Med existed. Also found out about the new plastic licences too, missed those coming out a few years back,

also, if you lost your log book, you may need to get re-endorsed for complex/high performance, etc.
Convince a CFI that you still know how to do that, and have them endorse your logbook


text:
What does the * (asterisk) next to radio and nav aid frequencies on Jeppesen charts refer to?
For Bournemouth, all radio frequencies and LOC IBMH are marked with an asterisk - *

Many other airports also have these markings, such as: Southampton, Alderney, Jersey, Guernsey, Exeter...
However, Cardiff doesn’t have an asterisk preceding to its radio frequencies:

But it does have one before LOC ICWA
What does an asterisk, preceding a frequency, refer to?

It means that this frequency is not always available (not always staffed). From the Introduction to Jeppesen Navigation Charts:

8 - Indicates the service is part time.

And further below:

Navaid boxes include the navaid name, identifier, Morse code, and frequency. A letter "D" indicates
DME capability with an asterisk indicating part time.

So tht would be the same for the LOC IBMH, the would turn off the ILS system?

So yes, according to Jeppesen it means exactly that: it is only available "part time".

As per UK AIP, EGHH is open 0630-2130. ATS follow AD operating hours, and IMBH is also marked as HO. EGFF on the other hand is open H24, however the ILS is still marked as HO (probably because only one ILS can be on at the time, the other will be off)

https://www.aurora.nats.co.uk/htmlAIP/Publications/2020-08-13-AIRAC/html/eAIP/EG-AD-2.EGHH-en-GB.html#EGHH-AD-2.3


text:
Why are so few heliports depicted on sectionals?
Pretty much every aerodrome, from an international airport to a private grass strip is depicted on a sectional chart. But there are few or no heliports shown. Why is this? Do helicopters have a separate sectional chart? It seems that even for a fixed wing pilot they would be useful as easily recognizable landmarks.
Just as a caveat, I don't have any actual paper sectionals. I am referring to what is shown at vfrmap.com. I have always presumed that their site is a good representation of the official charts, but it's possible there are things not shown online that are on the actual sectionals.

There are a few helicopter route charts for a select few metropolis area's.

@RonBeyer Ah, thx. I've seen a "Heli Route Chart" section in the FAA sectional guide, but I wasn't sure whet they were

A helicopter route chart is specific to navigation and is intended for areas with high concentrations of helicopter traffic (urban). The primary intent of the chart is not to map landing zones, but rather depict information relevant to helicopter operations and traffic. Not every helipad will be charted on the route charts.  (If one is planning survey flights, it is advisable to reference the helicopter route charts, as there is useful information which will help in working with helicopter traffic, such as common routes, altitudes, frequencies, etc.) and of course some of the area helipads.

I would disagree with the statement that pretty much every grass strip is charted.  This is common in CONUS, Alaska and Canada. There are at least 30 within a 10nm radius of mine which are not. The reasons for charting grass strips are usually:
1. You are inviting people.
2. You want to notice people that the strip is restricted.
3. You are in an area, where charting your strip for emergency use is a public service you choose to offer.
4. You have tenants on your strip, and you want to ease their navigation and those who may visit.
As for heliports being charted: If they are intended for public use, they frequently are.  They are also charted if they have allot of traffic (eg Hospital / EMS / police barracks). Many private helipads do not wish to invite the public, and there is no purpose in charting them.


text:
To do the holding pattern or not?

Full size: http://155.178.201.160/d-tpp/1710/06656ILD5.PDF
So for the plate, if we were approaching from the southwest on the ILS or the LOC/DME, would we have to conduct that holding pattern if we were cleared for the approach before reaching the IAF (not a straight in, not vectored, not timed, etc.)? Also, the MAP would be TFD 7.5 DME correct? How do I confirm that is the MAP?

@mins If you're cleared for the approach but the controller didn't clear you "straight in" then you still have to fly the hold (unless one of the other exceptions applies, as the OP said). That's what the page you linked to says, by the way. I suspect in this case it's required because of the obstacles, especially the ones to the southwest: the hold gives you a way to descend safely.

A controller can clear you for the procedure.  He cannot modify what is published by declaring it "straight in."  The hold here is required.

@acpilot - I interpreted the asker's language to mean "receiving vectors to final", which would not require the hold-in-lieu-of-procedure-turn.

Yes, you have to fly the hold.
If you're cleared for the approach, but you're not getting vectors to the final (or one of the other things you mentioned), the approach begins at the Initial Approach Fix (in this case, TFD) and you need to fly the full procedure, which will include the hold.

No, the missed approach point is 1,743 MSL (It's 7.5 DME for a localizer approach)
This is an ILS approach, so you go missed when you arrive at decision altitude and don't have one of the three required elements to descend further:

Visibility
Safe descent to landing
At least one of the required runway environment elements in sight

If you're shooting it as a localizer approach, you go missed when you cross the localizer and the needle flips. at 7.5 DME, a maneuver which is badly illustrated on this chart.  Thanks TomMcW!

To be pedantic about language, it is correctly called a "hold-in-lieu-of-procedure-turn" but in this answer I'm just calling it a hold.

Did you really mean when you cross the localizer? That doesn’t really make sense to me. When you say the needle flips Which needle are you referring to?

@TomMcW - Yep, I really did mean when the airplane passes over the localizer antenna. The CDI ("needle") will momentarily go to full scale deflection, indicating that you've crossed the localizer and it's time to go missed. I think that the to/from indicator may also flip, but I'm not positive about that.

So the MAP is at the far end of the runway? Can you provide a citation on that? Every other place I find says that the 7.5 DME is the MAP if not using the GS

@TomMcW - Oooooops, I didn't notice that it was a LOC/DME approach rather than a pure LOC approach.  Good catch!

The MAP on a LOC approach is never determined by simply watching the CDI for sensitivity changes - if nothing else, on a perfect approach you wouldn't see any change at all. A LOC will always show a TO flag, even on the Back Course, so that's no help.


text:
Are CTAF and UNICOM frequencies routinely recorded?
ATC communications are recorded for later examination by accident investigators or regulatory agencies. Are CTAF frequencies at untowered fields usually recorded? How about manned UNICOM frequencies?

They don't really have to: they have liveatc.net ;)

At my part-time-towered airport, we used to keep all frequencies keyed up overnight—including the Tower frequency, which becomes the CTAF after we close. Within the past year we were informed that, due to some legal agreement somewhere, we aren't supposed to record the frequencies when we aren't open and our new SOP is to deselect all frequencies (at least RX capability) as part of the closing checklist.


text:
Are there any restrictions on long overwater flights by private aircraft?
It is talked about in many questions here that (with the exception of older 3+ engine aircraft) airlines and their planes must be ETOPS certified if they are going to fly more than 60 minutes away from a suitable diversion airport.
Are there any similar restrictions for private flights?
If regulations differ, assume the flight is between the US and Europe in a US or European registered plane.

I am unable to find any ETOPS restrictions for private aircraft in the FAA FAR/AIM Part 91. The FAA Advisory Circular AC 91-70B is applicable for commercial aircraft operators. Anecdotally, general Aviation single-engine aircraft (Including helicopters) make oceanic journeys on a regular basis.

This level of regulation is best left to the insurance companies.

14 CFR § 91.501 - Applicability. - as long as you aren't getting paid, or does this not apply?

@Mazura - Part 91.501 - 91.536 are in Subpart F for large and turbine-powered aircraft. I have not found any ETOPS restrictions in this subpart. There are ETOPS restrictions specifically in Parts 121 & 135. Although, you can fly on a for-hire basis in Part 91, Parts 121 & 135 are for specific commercial operations.


text:
Are the replacement satellites for Iridium going to provide surveillance coverage?
Iridium satellites are to be replaced using SpaceX rockets.
Will the new LEO satellites be used for continuous tracking of commercial flights?

Wait, does this mean that iridium flares will stop being a thing?

@E.P. from Iridium: 'The Iridium NEXT satellites will launch in 2015-2017 and will have only one antenna instead of three. The new antennas offer increased data speed and capacity but are angled differently than the current design, and are therefore not likely to reflect much sunlight.' They missed the 2015 launch date, so the flares will around a bit longer but they will fade out.

The next generation of Iridium satellites will have ADS-B receivers installed on them which will be used to track properly equipped aircraft. The company providing this service is Aireon.
Most airliners are already equipped with ADS-B transmitters. From 2020 it is manadatory on the USA and in Europe to have ADS-B.
The first satellite were to be launched earlier this year, but so far nothing has been launched.


text:
Can autopilot track ILS without any internal heading reference?
I am asking about the internal design of the autopilot of a CRJ200 (no autoland).
I was flying an ILS approach when the AHRS heading started to drift rapidly by 30 degrees. The autopilot somehow was not able track the ILS and started to to fly an "S" turns. After this incident I had a discussion with TRE. He insisted that the ILS has nothing to do with heading. I think that it's impossible or very difficult to design an ILS tracking autopilot without internal heading reference.
How can an autopilot know that a plane is turning and how much without some internal heading reference? Can anybody provide any info on this topic and how the autopilot is implemented?

What aircraft/autopilot? There are huge differences in design. Most small aircraft A/P just blindly track the ILS, but an air transport approved for autoland has a very complicated A/P system to ensure safety.

CRJ200 no autoland

Yeah on an older system like Collins Proline once the loc is captured the ap is just responding to the loc deviation, and if you lose the loc it goes into heading hold.

Oh that problem.  That's related to a loc signal broadcast antenna issue at certain airports.  I forget the details.   Jazz was complaining about incidents at Pearson where their 200s were doing that (overshooting the loc and than turning back to crisscross it) and the capt had to disconnect and hand fly.

Your conclusion does have merit and makes sense. Although, logic can be programmed into the system to know how to navigate the LOC based on the Hertz received (90 vs 150). The FD/AP could then navigate by reference to equalizing these two signals within a certain distance from the center. Receiving a stronger signal would indicate which side you are on. While the weakening or strengthening of the other signal would indicate whether you are traveling toward or away from the center. You can determine which way to turn from this data. How much to turn would be a factor of ground speed.

Just in case you are unfamiliar with what I am talking about, review the FAA AIM section 1-1-9 on ILS navigation equipment.

I should have said bank angle hold hot heading hold.

@Andrius Was this happening while you were in green needles?

@John K. Yes green needles. I tried to look at the scientific papers about autopilots. As I understand at least bank angle change rate is required to track localizer. AP/FD cannot track ILS just by radio signal it has to know how plane is responding to control inputs

@Andrius Do you have the FMS4200 pilot's guide?  Dark blue small binder.

Can't imagine how you could get GPSS without AHRS.

Most autopilots in small aircraft blindly track the ILS (same for VORs) without any heading reference, which is actually simpler because heading can be substantially different from ground track, especially in crosswind. Technically speaking, the autopilot is a PD-controller, performing two tasks simultaneously:

When the needle wanders left, turn left, and when the needle wanders right, turn right. When the needle stops, the autopilot has found the correct heading. The actual position of the needle does not matter, only that it stops wandering. This is the loop that tracks heading, the differential (D-) part of the PD-controller.

When the needle is left of center, turn left, and when the needle is right of center, turn right. This is the loop that brings you back on the localizer, the proportional (P-) part of the PD-controller.

Both loops run simultaneously and the commanded turn rate is the sum of both. If the needle is left of center but wanders right, both loops cancel and the autopilot continues straight ahead. As the needle gets closer to the center, the proportional loop gets weaker and the differential loop wins, with the result that the aircraft turns slightly to the right and the needle stops wandering. The needle is now in the center and not wandering anymore, which means that the autopilot has successfully intercepted the localizer.
Note that while the autopilot does not use any heading reference, it still commands a turn rate and uses the turn coordinator and ailerons to fly the commanded turn rate. If your AHRS served as a turn coordinator for the autopilot, then the aircraft will veer off course if the AHRS fails.

Modern inertial navigation systems have a set of rate gyros (laser-ring or MEMS (vibrating)) and integrate the heading and attitude from the rates. So heading drifting means rate of turn did as well, because they are fed from the same gyro.

I'll give an answer with the caveat that I haven't used the system in over 10 years. So maybe do some additional research.
The Collins Proline Flight Director used on the 200 (it's not the Autopilot per se, it's the Flight Director telling the AP what to do), and most similar ones I would expect, needs heading, bank angle and turn rate data to anticipate and judge correction heading offsets, intercept angles, etc, to track navigation solutions whether on "white needles" (FMS navigation) or "green needles" (direct radio signal navigation like VOR or LOC).
If you think about it, it has to; the Flight Director is substituting for your brain, and it needs the same data, about where the airplane is headed and how much it's turning, that you would need to hand fly an approach on raw data.
If you're hand flying and drifting to the left of the loc, you mentally estimate the heading change needed to re-intercept the loc, fly the new heading and wait.  Without compass information you would have a pretty tough time doing it with any efficiency.  If your heading indication did the same thing while you were hand flying, you would probably end up doing something similar if you kept trying to fly the LOC by ignoring the heading indication.
So if the AHRS gyrocompass unit the Flight Director is slaved to starts to slew on its own, it'll get confused and go into a kind of software loop with the resulting S turns.  I would assume that selecting XFER to select the opposite FD/AHRS system fixed the problem.


text:
Why is flying in a slip uncomfortable?
It seems that flying a plane in a slip can make passengers uncomfortable.
What is it about that configuration that is unsettling?

I'd say this is when the acceleration is not aligned with the yaw axis (e.g. when the yaw damper is not active on an aircraft, or the pilot doesn't coordinate the rudder and the ailerons. In that case the ball will not be leveled and the weight will be sensed in a direction other than towards the aircraft floor.

If I saw a pilot wearing a slip, I would be very uncomfortable as a passenger!

weight will be sensed in a direction other than towards the aircraft floor. While casey & dave's answers are good, to me this makes the most sense.

@FreeMan that is what the first sentence of my answer says.

@casey - IANAP - effective gravity vector doesn't register right away :) Now that I reread it, yes, I get that.

A slip is uncoordinated flight and this shifts the effective gravity vector you experience.  Passengers in the back are also at a disadvantage without a visual horizon in front of them.  This can induce a mismatch between what the passengers can see versus what they are physically experiencing.  In some people this can cause discomfort and potentially vertigo.
Other discomfort can be psychological in nature that the airplane isn't behaving how they expect.  Passengers expect if a plane isn't turning that the wings are level.  If you are flying when the plane lands in a crosswind with a slight bank and touching down with one main gear, then the other main gear, many passengers will comment that the landing was incorrect because the main gear didn't all touch down together and the pilot was flying "sideways".  They don't realize the wind requires this technique and that the landing was in fact correct.  The perception of things not being right, however, can cause discomfort in some passengers.

It must be mostly psychological. When I have passengers in my car they experience 'slips' at every corner and seldom complain.

In a car you usually have visual cues that let you anticipate which way will feel like "up" at any moment. In a plane you have to get used to the fact that you'll get shaken around a bit without warning.

Slipping a plane is a form of uncoordinated flight during such a case the plane is inherently unstable and more susceptible to turbulence as caused by unstable air.
Some of the advantages of coordinated flight are

Coordinated flight is usually preferred over uncoordinated flight for the following reasons:

Comfort level of the passengers (the seat of their pants won’t be going this way and that).
Drag is kept to a minimum, helping to maximize the margin between actual air speed and stall speed.
Fuel will continue to be drawn equally from tanks in both wings,
  especially important after a long flight when fuel level may be low
  (of course you planned your flight to land with legal reserves,
  right?).
No cross controlling, no stalls, therefore no spins (bad, very bad).

To answer the question directly its the bumps that are unsettling however this is dependent on the situation. In calm air you, as a passenger would never know (but in calm air you really don't need to slip a plane). In a small GA plane where you can better see whats going on it may appear confusing on final approach the pilot is using heavy control inputs and the plane is moving straight (towards the runway that is)

Most of the answer is not about feeling uncomfortable at all, and the last paragraph claims you can't feel sideslips, when anyone who has flown a slideslip knows this is patently untrue.


text:
Do aircraft use the majority of their fuel to overcome friction?
It was asserted (tangentially) in this question that airliners use most of their fuel to overcome frictional losses.

Is that a true statement?

If so, approximately what percentage of fuel is used to overcome friction?
If not, what is the major use of fuel? (Beyond the obvious 'to run the engines'.)

By friction, do you mean surface friction based on the roughness of the surface on the aircraft, like rivets, or total drag?

Good question, @RonBeyer, and I'm not really sure. I'm just questioning the statement made in the other question, as it was unsupported, and didn't seem realistic to me. I would suspect that our usual, high quality answers will address both topics.

@vasin1987 Lift is a force. A force does not necessarily transfer energy, that depends on movement parallel to the force. Once the craft has reached maximum altitude the lift does not contribute any more potential energy to the craft. I don't think long distance flights could turn off their engines once they reach maximum altitude and reach their destination without burning anymore fuel. That energy has to go somewhere, and it isn't going into more potential energy.

@kasperd my comment does not go into detail about force or energy. Too complicate for me. Just suggest that part of fuel burn is used to create lift to overcome gravity. You need some force to overcome gravity.

@vasin1987 Force is not energy. You need force to overcome gravity, not energy.

@kasperd - the Force is from midichlorians and you need it to overcome the dark side.  ;)

For an aircraft in level flight, lift opposes the weight of the aircraft, and thrust from the engines opposes the drag of the aircraft.
One form of drag is skin friction drag. The statement you reference is in the context of skin heating, and the skin friction is the main way that the skin will be heating. Other significant sources of drag add energy to the air instead.
According to this paper, about half of an airliner's drag comes from skin friction. This estimation of cruise drag for a business jet shows a similar breakdown. About a third of the drag is induced drag, which is the side effect of lift.
To address the original statement, friction drag may account for the majority of fuel use, but not by very much. It is the largest source of drag but not always more than half of the total drag.

I realize that the question is rather vague, there's not much I can do about that, since I'm going off a quote from the other question. I suppose, though, that skin friction drag is the most likely cause of the friction being referenced. Does the majority of fuel use to overcome skin friction drag statement hold up?

@FreeMan I gave a shot at adding a statement about that.

No, the majority of the fuel is wasted on inefficiency of the engine.
Internal combustion engines like turbine engines are not exactly energy efficient. Most of the fuel is wasted by running the engine. Only about 35% to 40% of the energy from the fuel is converted to propulsive energy.  The rest of the energy from the fuel (~ 65%) is lost on heating up the atmosphere directly, excess kinetic energy in the exhaust stream, internal drag & friction of the engine and producing noise.
The remaining ~35% the energy is there to overcome the work done by drag.
This drag can be split into lift induced drag and parasitic drag.
It can also be split into pressure drag and friction drag.
For simplicity assume that all the lift induced drag is all pressure drag, and all parasitic drag is friction drag.
Aircraft usually cruise near the speed where drag is lowest. In such a situation, 50% of the drag is induced drag and 50% is parasitic drag. In practice cruise speed is a bit above the minimum drag speed, so the parasitic drag exceeds the induced drag. If our earlier assumption is correct, then over 50% of the drag would be friction drag.
That would bring the total estimates to:

65% wasted
20% friction drag
15% pressure drag

For example the GE90, the engine fitted on most Boeing 777s, produces a thrust of 70 kN in cruise flight of 250 m/s at a fuel consumption of 1.08 kg/s.
The propulsive power delivered by the engine is $70 \cdot 10^3 \cdot 250 = 17.5\cdot 10^6 \textrm{W}$.
Jet fuel has a specific heat of $43.15 \cdot 10^6 \textrm{J/kg}$
The energy consumption of the engines is thus:
$1.08 \cdot 43.15 \cdot 10^6 = 46.6 \cdot10^6\textrm{W}$
That gives an efficiency of 37.6%. This may seem poor but it is one of the most efficient engines available today.

Data sourcePDF for thrust, speed & consumption:

Well you are describing "frictional losses"... it's just within the engine, not on the skin.

@fooot Friction within the engine is a very tiny part of the 65%, not really significant.

Agreed as turbines are very different than internal combustion engines. The air goes through a series of compression and expansion (stators/compressors) as deltalima said the losses are due to thermal losses in the exhaust from the combustion chamber. The energy that is not converted to turning the turbine shaft. This is why oil is not used to lubricate the turbine engine like the internal combustion engine.

Aircraft like to fly near their optimum L/D ratio, where drag reaches its minimum. At that speed the drag is split evenly between induced (lift-related) and viscous drag. In a very rough approximation, half of the drag is indeed caused by friction.
However, if we look more closely, drag has more sources. Besides friction and induced drag, there is pressure drag due to flow separation at blunt, rear-facing surfaces. More separation could be caused by boundary layer effects, but this is highly aircraft- and angle-of-attack-specific. One could argue that this kind of pressure drag is also caused by friction.
If we now look at specific missions, more differences creep up:

An interceptor will try to reach a specific point in the shortest possible time. Here friction drag will easily be the dominant source of drag, induced drag is small and some of the fuel is needed for acceleration.
Airliners fly at optimum transport performance, which is faster than what optimum L/D would require. Friction drag here is indeed the biggest source of drag, but contributes maybe 50% to 60%.
Observation aircraft which want to optimize flying time will fly slower than what optimum L/D requires, especially if they use propellers. Now induced drag is responsible for the majority of fuel used.

That statement simplifies what's really happening to the basics of physics 101. Technically that statement is 100% true. It is also true for cars and ships: your car use most of its fuel to overcome friction.
Newton's first law: An object that is in motion stays in motion.
That means that once your car or an aircraft has reached the desired speed you should no longer need to run the engine and the car/aircraft will continue moving at a uniform speed until you apply the brakes. Is this how you drive your car? Obviously not. You need to depress the throttle all the way (or at least most of the way).
So what gives? Newton says that the car should continue moving and therefore you should be able to turn off your engine for 99% of your trip! The answer is friction, it all its various forms.
Some people may say: "but most of the energy in flight is used to generate lift, not overcome friction". But lift comes from friction. Lift causes drag, specifically induced drag. But this drag is only possible due to friction - the friction of air with itself. We quantify this "friction" as viscosity. Fluids that are completely frictionless have zero viscosity (such things do exist: they're called superfluids) and it's impossible to generate lift in such fluids. Fortunately air is viscous so airplane wings can work in air.
So.. technically it's true - any moving vehicle spends the majority of its fuel to overcome friction. But it's not really useful from an engineering perspective.
There is an exception though: spaceships. Since friction is almost zero in the vacuum of space spaceships burn their fuel only at the beginning of the trip and at the end to slow down. 99% of the time the engines on a spaceship is turned off and the ship merely coast along thanks to Newton's first law.

Please do not take the papers on friction and the Kutta condition too seriously. Lift-induced drag has really nothing to do with friction. If those paper authors would had looked at inertial forces, too, they would had realized that they don't need friction to explain the Kutta condition.

@PeterKämpf: But those inertial forces are mainly possible due to viscosity. Without viscosity there would be no lift. Without lift there would be no lift induced drag.

@slebetman: Why would lift be impossible without viscosity? Imagine an aircraft moving through an idealized inviscid atmosphere consisting of massive molecules that bounce elastically off the perfectly smooth surface of the aircraft but don't interact with each other except at long timescales, to make sure their velocities before the aircraft arrives follow a Maxwell-Boltzmann distribution. If our aircraft flies with a positive angle of attack, it will still be able to bounce molecules downwards, generating lift (and induced drag too) -- but there will be no friction.

@HenningMakholm: Without viscosity, and if the molecules are indeed fluid (instead of ping pong balls) then each molecule will also move up again to its original position after being bounced down (actually this happens even with viscosity). Without viscosity, the amount of up force generated by the molecule bouncing down is exactly equals to the amount of down force generated by the molecule moving back up - generating exactly zero lift. Of course, real-world superfluids may not exactly generate the same amount of force both ways so physical superfluids do generate lift but not much.

@slebetman: Which force or interaction would make each molecule "move up again to its original position"?

@HenningMakholm: Non viscosity. The molecule moving down creates an absence of molecules above it. This creates a vacuum. In a viscous fluid some of the molecules from above will be sucked in to this region adding to total lift. In non viscous fluids most of the molecules that have moved down will instead move up to fill the void because moving down creates a high pressure region that pushes on the molecules back up.

@slebetman: I'm specifying that the molecules don't interact on short timescales, so there's nothing that can change the velocity of each molecule after it has bounced off the wing and started moving downwards. More importantly, though: Bouncing molecules downwards from the wing means that downwards momentum is being transferred from the aircraft to the molecules in the gas. If, as you claim, no lift is being generated, that momentum will have to be returned to the aircraft. How does that happen?

@HenningMakholm: Then that's not a fluid. So OK. Under your specification airfoils can certainly create lift when flown in an atmosphere of pingpong balls. You yourself have failed to account for conservation of momentum. In a non-viscous superfluid, molecules that have bounced downwards from the wing will move back up to its original position. How does the wing gain momentum?

@slebetman: The wing gains momentum because more molecules hit it on the underside than on the top, due to moving through the air at a positive angle of attack. What happens to those molecules afterwards is irrelevant to lift generation -- it doesn't influence what the wing experiences anyway.

@HenningMakholm: So far we've been arguing theories. I submit an actual physical experiment of measuring lift on airfoils in a superfluid helim "wind tunnel" that found lift to disappear at low velocities and extremely small even at higher velocities. This is not theory, it's simply how nature behaves: http://thesis.library.caltech.edu/455/1/Craig_pp_1959.pdf

A jet engine is a Brayton cycle device and has fundamental limits on the performance. From the diagram in the source looks like for the ideal theoretical engine with no friction at all and pressure ratio about 30 (Boeing 747 engine), the efficiency limit is somewhat 60 %.
This means that about 40 % of the energy dissipates as the heat, the engine cannot convert it. It is not lost due friction. This is significant percent but less than a half.
About some WWII jet bomber with pressure ratio about 3 it is possible to say that the major energy loss is because of the engine thermodynamics, not because of the friction.


text:
What airport has this walkway over a taxiway?
I saw this image posted in another question. What airport is this?

This image was taken at London Gatwick. The bridge connects two portions of the North Terminal, right next to where the North Terminal is labeled on this map:

London Gatwick claims to be the first airport to have such a feature. As can be seen in the photo, it is the largest in the world, high enough for a 747 to pass underneath.
This is not the only airport to have such a feature, though. Denver International also has a bridge (picture) over the taxiway connecting the terminal building with Concourse A. This one is not as high as the bridge at Gatwick and can't clear anything larger than a 737.

Thanks, fooot! I got busy wandering around London area airports on Google maps, and forgot to come back to give you an upvote...

I tried a TinEye search, but all it came up with was the imgur link of the original post

@FreeMan Interesting, I used Google and it identified Gatwick (and found the article I linked to).

You can see it in this Google Maps image -- they even took the photo just as a plane was going under the bridge.

KLIA2 in Kuala Lumpur also has sky bridge


text:
How does take off mass impact induced drag?
In this answer to another question, it was stated that:

Take-off mass: If you take no payload, the aircraft will produce less induced drag and reach a slightly higher range

How does a change of weight inside the same shaped container increase induced drag, since the air doesn't come in contact with the cargo?

For the same aircraft speed and an horizontal trajectory:

When the aircraft is lighter, less lift is required.
To decrease the lift, the angle of attack needs to be reduced (said otherwise: the aircraft flies more horizontal).
A smaller AoA creates less induced drag.

Lift and drag coefficients as a function of the angle of attack are represented in the following diagram.

(Source)
The ratio L/D is also represented, with its maximum L/D max. L/D max is an economical angle of attack. After L/D max, a gain in lift is at the expense of a larger increase in induced drag.
Side-effect of reduced drag:

The thrust can be reduced to achieve the previous speed.
The range is increased thanks to the thrust reduction.

For a more accurate representation of lift and drag coefficients against the angle of attack, and additional information: Lift and drag curves for the wing.

Induced drag is caused by lift. (historically, Induced Drag was named "lift induced drag").
If weight(mass) of the aircraft decreases, the lift required to fly the aircraft decreases. And the drag associated to that lift also decreases.
The quoted statement is true, but "slightly" can be discussed. Because the increase in range depends a lot on how much payload the aircraft could carry. (If it's %50 of the max takeoff weight, the range could increase a lot).

OK, "slightly" is only true for aircraft with good aerodynamics. Only if creating more lift does not impact drag significantly, "slightly" is justified. But I assumed that today we should be able to meet that goal without much effort.

Two ways of generating more lift, which is needed to carry more weight: 1. increase angle of attack. 2. Increase speed with same angle of attack. Both create more drag, there for both require more gallons per hour to fly.
Because of higher AOA requirement for a given amount of lift at a given speed, a more heavily loaded aircraft will stall at a higher airspeed.  This is why, when taking off and landing, it is a good idea to know the stall speed for your weight, and add in your safety margin accordingly.


text:
What callsign would a medical emergency flight use?
I see medical emergency helicopters taking off and landing several times a day from the hospital near my office. As I understand from an earlier question, they are probably flying VFR, below controlled airspace and likely without ADS-B.
I would assume, however, that these flights are in touch with the local ATC, and they are certainly announcing their presence on the locally monitored channel(s). Is there a particular set of call signs or other indicators that are used by these flights to indicate to other traffic that, while this flight itself is not in any sort of mayday situation, it needs priority handling and that everyone else needs to get out of the way as lives depend on the speed of this particular flight?
I am asking particularly for the USA/FAA, but would be interested to know if there are differences in other countries around the world.

The variety of callsigns used for medical flights are covered in the AIM 4-2-4:

b. Air Ambulance Flights.
Because of the priority afforded air ambulance flights in the ATC system, extreme discretion is necessary when using the term “MEDEVAC.” It is only intended for those missions of an urgent medical nature and to be utilized only for that portion of the flight requiring expeditious handling. When requested by the pilot, necessary notification to expedite ground handling of patients, etc., is provided by ATC; however, when possible, this information should be passed in advance through non−ATC communications systems.

Civilian air ambulance flights responding to
  medical emergencies (first call to an accident scene,
  carrying patients, organ donors, organs, or other
  urgently needed lifesaving medical material) will be
  expedited by ATC when necessary. When expeditious
  handling is necessary, include the word
  “MEDEVAC” in the flight plan per paragraphs 5−1−8
  and 5−1−9. In radio communications, use the call
  sign“MEDEVAC,” followed by the aircraft registration
  letters/numbers.
  EXAMPLE− MEDEVAC Two Six Four Six.
Similar provisions have been made for the use
  of “AIR EVAC” and “HOSP” by air ambulance
  flights, except that these flights will receive priority
  handling only when specifically requested.
Air carrier and air taxi flights responding to
  medical emergencies will also be expedited by ATC
  when necessary. The nature of these medical
  emergency flights usually concerns the transportation
  of urgently needed lifesaving medical materials
  or vital organs. IT IS IMPERATIVE THAT THE
  COMPANY/PILOT DETERMINE, BY THE
  NATURE/URGENCY OF THE SPECIFIC
  MEDICAL CARGO, IF PRIORITY ATC ASSISTANCE
  IS REQUIRED. Pilots must include the word
  “MEDEVAC” in the flight plan per paragraphs 5−1−8
  and 5−1−9, and use the call sign “MEDEVAC,”
  followed by the company name and flight number for
  all transmissions when expeditious handling is
  required. It is important for ATC to be aware of
  “MEDEVAC” status, and it is the pilot’s responsibility
  to ensure that this information is provided to ATC.
  EXAMPLE−
  MEDEVAC Delta Thirty−Seven.

This is age old, but this phrase "and to be utilized only for that portion of the flight requiring expeditious handling" just caught my attention. Which part of a flight would not require expeditious handling? Going to pick up a patient? It's still urgent that they get there as minutes do matter. Or does that refer to a non-emergency, repositioning/training/otherwise flight performed by an air ambulance?

"and to be utilized only for that portion of the flight requiring expeditious handling", I assume this would mean for a flight from an airport to the patent and back to hospital helipad is important, the repositioning flight back to the airport is not. Most helicopter pilots count a flight as the whole process, including incidental landings etc.

@FreeMan If the patient dies en route, you’re supposed to cancel MEDEVAC status.

The US call sign is "MEDEVAC." It used to be "LIFEGUARD," but was changed in 2012 as part of the transition to ICAO flight plans, which suggests that "MEDEVAC" could be a standard (though I'm not sure if it is).

"Helimed" is the most common callsign for U.K. air ambulances, e.g. Helimed 42.
When not on an emergency call or when returning to base, they would use an abbreviated callsign, e.g. Hotel Mike 42.
They also usually operate as Special VFR flights, meaning they can fly using instruments and ATC vectors if required and they will be in touch with ATC at all times, mainly for traffic avoidance (other aircraft are moved to allow the ambulance clear passage).

Welcome to aviation.SE!

In Boston, where I live, medivacs use custom call signs that they pick for themselves. Medflight uses the generic "Med One", "Med Two", "Med Three". "Lifeflight" that is run by the University of Massachusetts uses "Lifeflight" as their callsign. Northern Massachusetts is covered by the Dartmouth Hitchcock Advanced Response Team. They use "DHART".

I little off base, but when I flew air ambulances in Southern Louisiana, where helicopter traffic is extremely heavy because of oil field and offshore use, I used the personal call sign "Savior 6" as a personal moniker. I was an RN and Paramedic. Helicopter call signs were known to be Aircare and Acadian Ambulance's AIRMED.